The present invention relates to an internal combustion engine that is capable of operating in accordance with two combustion types of ignition, namely, spark ignition and compression ignition, and in particular it relates to an internal combustion engine that operates to switch between a 2-cycle compression ignition and a 4-cycle compression ignition in accordance with operating conditions of the engine and environmental conditions.
A compression ignition type of internal combustion engine has advantages of better fuel economy (gas mileage) because of high compression ratio and lower NOx exhaust amount because of low combustion temperature. In order to induce a compressed self-ignition, it is required to raise a gas temperature in a combustion chamber beyond a predetermined temperature. For that purpose, such schemes as intake air heating, internal EGR and the like are generally used. When the temperature in the combustion chamber is lower than a predetermined temperature (that is, at a low-load operation time), the operation of the engine needs to be switched to the spark ignition type of combustion because the temperature may not be high enough even around the top dead center (TDC). Otherwise, misfiring would take place because of low temperature (Japanese Patent Application Unexamined Publication (Kokai) No. 2000-87749).
In general, however, the spark ignition combustion has worse fuel economy and larger exhaust amount of the nitrogen oxides (NOx) than the compression ignition combustion. Therefore, there exists a need for carrying out compression ignition combustion even when the temperature in the cylinder is low.
Thus, it is an objective of the present invention to provide a compression ignition type of internal combustion engine in which an operation range allowing for the compression ignition combustion is expanded.